Unprecedented 25-year study traced forest carbon through air, trees, soil, and water
HARVARD UNIVERSITY
Climate change has increased the productivity of forests, according to a new study that synthesizes hundreds of thousands of carbon observations collected over the last quarter century at the Harvard Forest Long-Term Ecological Research site, one of the most intensively studied forests in the world.
The study, published today in Ecological Monographs, reveals that the rate at which carbon is captured from the atmosphere at Harvard Forest nearly doubled between 1992 and 2015. The scientists attribute much of the increase in storage capacity to the growth of 100-year-old oak trees, still vigorously rebounding from colonial-era land clearing, intensive timber harvest, and the 1938 Hurricane – and bolstered more recently by increasing temperatures and a longer growing season due to climate change. Trees have also been growing faster due to regional increases in precipitation and atmospheric carbon dioxide, while decreases in atmospheric pollutants such as ozone, sulfur, and nitrogen have reduced forest stress.
“It is remarkable that changes in climate and atmospheric chemistry within our own lifetimes have accelerated the rate at which forest are capturing carbon dioxide from the atmosphere,” says Adrien Finzi, Professor of Biology at Boston University and a co-lead author of the study.
The volume of data brought together for the analysis – by two dozen scientists from 11 institutions – is unprecedented, as is the consistency of the results. Carbon measurements taken in air, soil, water, and trees are notoriously difficult to reconcile, in part because of the different timescales on which the processes operate. But when viewed together, a nearly complete carbon budget – one of the holy grails of ecology – emerges, documenting the flow of carbon through the forest in a complex, multi-decadal circuit.
“Our data show that the growth of trees is the engine that drives carbon storage in this forest ecosystem,” says Audrey Barker Plotkin, Senior Ecologist at Harvard Forest and a co-lead author of the study. “Soils contain a lot of the forest’s carbon – about half of the total – but that storage hasn’t changed much in the past quarter-century.”
The trees show no signs of slowing their growth, even as they come into their second century of life. But the scientists note that what we see today may not be the forest’s future. “It’s entirely possible that other forest development processes like tree age may dampen or reverse the pattern we’ve observed,” says Finzi.
The study revealed other seeds of vulnerability resulting from climate change and human activity, such as the spread of invasive insects.
At Harvard Forest, hemlock-dominated forests were accumulating carbon at similar rates to hardwood forests until the arrival of the hemlock woolly adelgid, an invasive insect, in the early 2000s. In 2014, as more trees began to die, the hemlock forest switched from a carbon “sink,” which stores carbon, to a carbon “source,” which releases more carbon dioxide to the atmosphere than it captures.
The research team also points to extreme storms, suburbanization, and the recent relaxation of federal air and water quality standards as pressures that could reverse the gains forests have made.
“Witnessing in real time the rapid decline of our beloved hemlock forest makes the threat of future losses very real,” says Barker Plotkin. “It’s important to recognize the vital service forests are providing now, and to safeguard those into the future.”
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It has been 66 years since the last real tree-snapping hurricane passed through this area, as “Carol” in 1954. Prior to that the 1938 hurricane did worse. But before that you have to peer back over a century to find the prior tree-snapper. They are so rare that, just before the 1938 hurricane, some foolish “authority” stated “Hurricanes never hit New England.” They do. They may be rare, but they are natural. And they demolish forests in a way I can’t really imagine, for I’ve never seen it.
I can wander the woods and see evidence of both Carol and the 1938 Hurricane. One rather neat thing is stripes of green moss among the brown pine needles of a forest floor, all striping in the same direction. That is all that is left of rotted tree trunks. At the end of each green stripe is a pile of stones. That is all that is left of the root ball which was torn from the ground.
Another rare event involves an especially warm “Indian Summer” with a stream of air basically coming along a vector from the deserts of Arizona, when our forests ordinarily are drenched by former tropical storms and the first nor’easters of the autumn. The summer dryness extends into autumn, with the falling leaves are crisp and dry, and then some fool ignores Smokey The Bear. Then New England experiences a California fire, and in the past we have been inept at slowing the blazes spread. In 1947 several towns were wiped out, but my favorite tale was told by an old fisherman who was out to sea as the fire roared over Mount Desert Island in Maine. He stated that the fire was so intense that, when it reached the end of the island and you would think it would run out of fuel, it continued on out to sea as a fireball over the water. Yowza!
When you visit Mount Desert Island now you see verdant forests. You’d never believe such a fire could occur, and would be a perfectly natural event, if it happened again.
These young whippersnappers need to study history. Then they may understand no “equation” involving “carbon flow” and “carbon storage” in New England can be called complete until it includes one whopper of a hurricane, and one whopper of a forest fire.
Caleb says:
The summer dryness extends into autumn, with the falling leaves are crisp and dry, and then some fool ignores Smokey The Bear.
Good to see you post, Caleb. What you describe happened to some areas of West Virginia back in the fall of 1991. Drought since August & extending thru October caused forest-fires — smoke could be smelled for weeks where I was in southwest VA, but finally got put out by a cold rain first couple days of November.
Mount Desert Island. Now that’s a confused identity.
“increasing temperatures and a longer growing season”.?? I’d wager that in the Harvard Forest any changes, if any in the plus direction, are minuscule at best. More garbage.
“Our data show that the growth of trees is the engine that drives carbon storage in this forest ecosystem,”
Really? Wow! Well I never…..Amazing ”data” you have there!
How did they think an increase in mass was possible in a tree?
And trees don’t ”store” carbon by the way, they use it to make more tree.
A NASA Earth Observatory internet offering entitled “Satellite Detects Human Contribution To Atmospheric CO2” dated 2014-2016 purported to show a mapping of human induced atmospheric CO2 in the United States and other countries. The U.S. map showed that almost all of the “human induced CO2” occurred in the cold, moist Northeastern and warm rainy Southeastern quadrants of the country. The semi- arid Western half of the U.S. showed little or no presence of human induced CO2. The most pronounced areas of human induced CO2 did not appear at centers of human concentration but rather in those areas of more intense broad leaf vegetation especially forests containing broad leaf trees.